Summary: Researchers are turning to jellyfish and fruit flies to explore the motivation to feed and shed new light on the mechanisms underlying feeding regulation.

Source: Tohoku University

Decades of research have shown that the motivation to eat, i.e. hunger and feelings of fullness, is controlled by hormones and small proteins called neuropeptides. They are found in a wide range of organisms such as humans, mice and fruit flies.

Such widespread occurrence suggests a common evolutionary origin. To explore this phenomenon, a research group turned to jellyfish and fruit flies, finding surprising results.

Although jellyfish share a common ancestor with mammals at least 600 million years ago, their bodies are simpler; they possess diffuse nervous systems called neural networks, unlike mammals which have more concrete structures like a brain or ganglia. Yet jellyfish possess a rich repertoire of behaviors, including elaborate foraging strategies, mating rituals, sleep, and even learning.

Despite their prominent position in the tree of life, these fascinating creatures remain understudied and almost nothing is known about how they control their food intake.

The group, led by Hiromu Tanimoto and Vladimiros Thoma from Tohoku University’s Graduate School of Life Sciences, focused on Cladonema, a small jellyfish with branching tentacles that can be bred in the lab. These jellyfish regulate their amount of food according to their hunger.

“First, to understand the mechanisms underlying feeding regulation, we compared gene expression profiles in starved and fed jellyfish,” Tanimoto said.

“Feeding state altered the expression levels of many genes, including some that code for neuropeptides. By synthesizing and testing these neuropeptides, we found five that reduced the feeding of hungry jellyfish.

The researchers then looked at how one such neuropeptide, GLWamide, controls eating. Detailed behavioral analysis revealed that GLWamide inhibited tentacle shortening, a crucial step for the transfer of captured prey to the mouth. When the researchers tagged GLWamide, they found that it was present in motor neurons located in the bases of the tentacles and that it fueled increased levels of GLWamide.

This led to the conclusion that, in Cladonema, GLWamide acts as a satiety signal – a signal sent to the nervous system that the body has had enough food.

Yet researchers’ quest to explore the evolutionary significance of this discovery did not end there. Instead, they turned to other species. The feeding habits of fruit flies are regulated by the myoinhibitory peptide neuropeptide (MIP).

Fruit flies lacking MIP eat more food and eventually become obese. Interestingly, MIP and GLWamide share similarities in their structures, which suggests that they are evolutionarily related.

“Given that the functions of GLWamide and MIP have been conserved despite 600 million years of divergence, this led us to wonder if it was possible to interchange the two,” Thoma said. “And we did just that, first giving jellyfish MIP and then expressing GLWamide in flies that didn’t have MIP.”

Surprisingly, MIP reduced Cladonema feeding, just as GLWamide had. Moreover, GLWamide in flies eliminated their abnormal overfeeding, indicating the functional conservation of the GLWamide/MIP system in jellyfish and insects.

Tanimoto notes that their research highlights the deep evolutionary origins of a conserved satiety signal and the importance of exploiting a comparative approach. “We hope that our comparative approach will inspire focused investigation of the role of molecules, neurons, and circuits in regulating behavior in a larger evolutionary context.”

About this neuroscience research news

Author: Press office
Source: Tohoku University
Contact: Press Office – Tohoku University
Picture: The image is credited to Hiromu Tanimoto

Original research: Access closed.
“At the origin of appetite: GLWamide in jellyfish represents an ancestral satiety neuropeptide” by Hiromu Tanimoto et al. PNAS

Abstract

At the origin of appetite: GLWamide in jellyfish represents an ancestral satiety neuropeptide

Food intake is regulated by the internal state. This function is mediated by hormones and neuropeptides, which are best characterized in popular model species. However, the evolutionary origins of these diet-regulating neuropeptides are poorly understood. We used jellyfish Cladonema to answer this question.

Our combined transcriptomic, behavioral, and anatomical approaches identified GLWamide as a feeding-suppressing peptide that selectively inhibits tentacle contraction in this jellyfish. I

n the fruit fly Drosophila, myo-inhibitory peptide (MIP) is a satiety-related peptide. Surprisingly, we found that GLWamide and MIP were fully interchangeable in these evolutionarily distant species for feeding suppression.

Our results suggest that the satiety signaling systems of various animals share an ancient origin.